# #37500 \[BC-Low] Blocklist can be circumvented due to incorrect blocking logic in \`request\_decider::c **Submitted on Dec 6th 2024 at 12:31:58 UTC by @n4nika for** [**Attackathon | Stacks**](https://immunefi.com/audit-competition/stacks-attackathon-1) * **Report ID:** #37500 * **Report Type:** Blockchain/DLT * **Report severity:** Low * **Target:** * **Impacts:** * A bug in the respective layer 0/1/2 network code that results in unintended smart contract behavior with no concrete funds at direct risk ## Description ## Note to immunefi This issue was discussed with the Stacks team on discord and I was asked by @Evonide to submit it without the need for a PoC, which is why none is provided on this issue ## Summary `request_decider::can_accept_deposit_request` currently returns `Ok(true)` if there is at least one non-blocklisted address as an input to a deposit UTXO. This means anyone can circumvent the blocklist by adding a tiny non-blocklisted UTXO as an input to their deposit request. ## Finding Description `can_accept_deposit_request` uses the following code to determine whether a certain UTXO can be accepted: ```rs async fn can_accept_deposit_request(&self, req: &model::DepositRequest) -> Result { // [getting addresses from the request] let responses = futures::stream::iter(&addresses) .then(|address| async { client.can_accept(&address.to_string()).await }) .inspect_err(|error| tracing::error!(%error, "blocklist client issue")) .collect::>() .await; // If any of the inputs addresses are fine then we pass the deposit // request. let can_accept = responses.into_iter().any(|res| res.unwrap_or(false)); Ok(can_accept) } ``` As we can see, we create a `responses` vector with elements for each input address, either being `true` if the address can be accepted or `false` if it should be rejected. Then `can_accept` is determined by using `.any` on the responses. `any` returns `true` if there is at least one `true` element in `responses`. ## Impact Say a user has a big UTXO which is blacklisted but wants to deposit it. They can just create a deposit request including a very small UTXO from a non-blocklisted address, allowing them to successfully deposit their bitcoins to Stacks from an address which should not be allowed to do so. ## Mitigation Consider using `.all` instead of `.any` to ensure none of the inputs to the UTXO come from blocklisted addresses. ## Proof of Concept Omitted due to direct request from Stacks team --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://reports.immunefi.com/stacks-i-attackathon/37500-bc-low-blocklist-can-be-circumvented-due-to-incorrect-blocking-logic-in-request_decider-can_ac.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.